54 A CHAPTER IN THE PHYSICAL GEOGRAPHY OF THE PAST. 
until, owing to a series of small folds, it is brought to the surface 
again some 20 miles to the south-east on the northern margin of 
Charnwood Forest. We there find it in eight small patches, of 
which that of Ticknall is the most northerly, and that of Grace 
Dieu the most southerly. 
But the rock has undergone a great change between Derbyshire 
and Charnwood. Instead of the thick, massive beds of lime- 
stone, of which we hive never seen the base, and which must be 
at least from 4,000 to 5,000 feet thick in North Derbyshire, we 
find a rapid tailing off in thickness as Charnwood is reached ; a 
tailing off which at Grace Dieu, only 20 miles south of the 
Derbyshire hills, Aas reduced the thickness to about 40 feet. At the 
same time the rock loses somewhat its purity, and becomes rather 
more earthy in character, but there is no intercaldation of sandy 
beds. At Ticknall, as some of you will remember, we have 
unmistakable evidence of the shelving nature of the bottom 
upon which the limestone was deposited. 
Taking all the evidence together, there can be no doubt that 
we are approaching once more a coast dine, for the attenuation 
of the Mountain Limestone cannot be due to denudation, since 
we find it overlaid by the Limestone Shales and Millstone Grit. 
This new southern land must have been of an entirely different 
character from the continent bounding the sea to the north. 
That there must have been clear water nearly close up to the 
shore is proved by the existence of an organically formed lime- 
stone very near the old coast line. That the land must have been 
of too small an extent to give rise to any great streams, is shown 
by the absence of any material incoming of sedimentary strata as 
the southern shore is approached. This southern land was in 
fact an zs/and bounded by a rocky coast. Of this island the 
northern portion of the Charnwood area was part, and there is 
not much difficulty by the aid of natural exposures, and by the 
results of borings, in determining approximately its extent and 
shape. It must have been long, narrow, and rocky, and extended 
from what is now the east coast of Ireland, through the Central 
Midlands, to an indeterminate point eastward, 
